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mutex.go
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mutex.go
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// Copyright 2016 CoreOS, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package concurrency
import (
"sync"
"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
v3 "github.com/coreos/etcd/clientv3"
)
// Mutex implements the sync Locker interface with etcd
type Mutex struct {
client *v3.Client
pfx string
myKey string
myRev int64
}
func NewMutex(client *v3.Client, pfx string) *Mutex {
return &Mutex{client, pfx, "", -1}
}
// Lock locks the mutex with a cancellable context. If the context is cancelled
// while trying to acquire the lock, the mutex tries to clean its stale lock entry.
func (m *Mutex) Lock(ctx context.Context) error {
s, err := NewSession(m.client)
if err != nil {
return err
}
// put self in lock waiters via myKey; oldest waiter holds lock
m.myKey, m.myRev, err = NewUniqueKey(ctx, m.client, m.pfx, v3.WithLease(s.Lease()))
// wait for deletion revisions prior to myKey
err = waitDeletes(ctx, m.client, m.pfx, v3.WithPrefix(), v3.WithRev(m.myRev-1))
// release lock key if cancelled
select {
case <-ctx.Done():
m.Unlock()
default:
}
return err
}
func (m *Mutex) Unlock() error {
if _, err := m.client.Delete(m.client.Ctx(), m.myKey); err != nil {
return err
}
m.myKey = "\x00"
m.myRev = -1
return nil
}
func (m *Mutex) IsOwner() v3.Cmp {
return v3.Compare(v3.CreatedRevision(m.myKey), "=", m.myRev)
}
func (m *Mutex) Key() string { return m.myKey }
type lockerMutex struct{ *Mutex }
func (lm *lockerMutex) Lock() {
if err := lm.Mutex.Lock(lm.client.Ctx()); err != nil {
panic(err)
}
}
func (lm *lockerMutex) Unlock() {
if err := lm.Mutex.Unlock(); err != nil {
panic(err)
}
}
// NewLocker creates a sync.Locker backed by an etcd mutex.
func NewLocker(client *v3.Client, pfx string) sync.Locker {
return &lockerMutex{NewMutex(client, pfx)}
}